[contingencies]

Why not work around the expectation and simply migrate offline? (eg. dump DB, hack dumpfile/stream, load new CSV?) While you may lose instantaneous constraint validation, it would almost certainly be faster and allow you to work with known and well tested tools. Conforms to the Unix design philosophy: "Store data in flat text files." / "Write programs to handle text streams, because that is a universal interface." http://github.com/globalcitizen/taoup

Since you were nominally optimizing for migration, a zoom-out perspective may be to note that upgrading SQLite3 versions vs. upgrading major RDBMS versions is trivial/fast, relatively rarely required, also cohabitation of multiple versions works a lot easier, any kind of CI/CD process is going to be orders of magnitude faster and use much less CPU/memory/disk space, which means smaller build artifacts and thus faster transfer/download.